<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .change {
            background-color: aqua;
            color: brown;
            font-size: large;
        }
    </style>
</head>
<body>
    <div>
        哈哈
    </div>
    <script>
        var box = document.querySelector('div');
        box.onclick = function() {
            // 增加类名给样式
            this.className = 'change';
        }
    </script>
</body>
</html>